Transesterification of dimethyl oxalate with phenol over a MoO3/SiO2 catalyst prepared by thermal spreading

MoO3/SiO2 catalysts for the transesterification of dimethyl oxalate (DMO) with phenol were prepared by both the thermal spreading (TS) and incipient wetness impregnation methods. The results showed that the 10%MoO3/SiO2 catalyst prepared by TS (10%MoO3/SiO2-TS) exhibited higher catalytic performance compared with the 10%MoO3/SiO2 catalyst prepared by incipient wetness impregnation (10%MoO3/SiO2-C). The catalysts were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, pyridine-IR spectroscopy, and NH3 temperature- programmed desorption. These analyses indicated that weak Lewis acid sites were formed on the catalyst surfaces and that the Mo species were present as monomeric MoO3 rather than as isolated molybdenum oxide or polymolybdate species on both catalysts, although the 10%MoO3/SiO2-TS exhibited better dispersion of MoO3 and a higher surface Mo content than the 10%MoO3/SiO2-C. Under the optimal transesterification reaction conditions (1.2 g 10%MoO3/SiO2-TS, T = 180 °C, n(DMO)/n(phenol) = 2, t = 4 h), the conversion of phenol was 70.9%, and the yields of methyl phenyl oxalate and diphenyl oxalate were 63.1% and 7.7%, respectively.